U.S. patent number 8,688,012 [Application Number 13/287,578] was granted by the patent office on 2014-04-01 for developing device and image forming apparatus.
This patent grant is currently assigned to Ricoh Company, Ltd.. The grantee listed for this patent is Hiroshi Kikuchi, Natsumi Matsue, Junichi Matsumoto, Tomoya Ohmura, Yasuo Takuma. Invention is credited to Hiroshi Kikuchi, Natsumi Matsue, Junichi Matsumoto, Tomoya Ohmura, Yasuo Takuma.
United States Patent |
8,688,012 |
Matsumoto , et al. |
April 1, 2014 |
Developing device and image forming apparatus
Abstract
In a disclosed developing device, a developing part includes a
developer carrier for circulating a developer inside the developing
part and for supplying the developer to an image carrier, a
developer supply member for supplying the developer to the
developer carrier, and a developer collection member for collecting
the developer which is not used. A developer stirring part is
arranged at a different position from a position of the developing
part. A developer conveyance part carries the developer by an air
conveyance in a developer conveyance path from the developer
stirring part to the developing part. A developer detection part
includes an opening which communicates between the developer supply
member and the developer collection member, is arranged at a
downstream side in a flow direction of the developer below and near
the developer supply member, and detects whether the developer
exists in a vicinity of the developer supply member.
Inventors: |
Matsumoto; Junichi (Kanagawa,
JP), Ohmura; Tomoya (Kanagawa, JP), Takuma;
Yasuo (Kanagawa, JP), Kikuchi; Hiroshi (Kanagawa,
JP), Matsue; Natsumi (Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Matsumoto; Junichi
Ohmura; Tomoya
Takuma; Yasuo
Kikuchi; Hiroshi
Matsue; Natsumi |
Kanagawa
Kanagawa
Kanagawa
Kanagawa
Kanagawa |
N/A
N/A
N/A
N/A
N/A |
JP
JP
JP
JP
JP |
|
|
Assignee: |
Ricoh Company, Ltd. (Tokyo,
JP)
|
Family
ID: |
46019729 |
Appl.
No.: |
13/287,578 |
Filed: |
November 2, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120114349 A1 |
May 10, 2012 |
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Foreign Application Priority Data
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Nov 4, 2010 [JP] |
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2010-247846 |
Nov 4, 2010 [JP] |
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2010-247850 |
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Current U.S.
Class: |
399/254; 399/258;
399/27 |
Current CPC
Class: |
G03G
15/0879 (20130101) |
Current International
Class: |
G03G
15/08 (20060101) |
Field of
Search: |
;399/254,256,258,27,53 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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8036294 |
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Feb 1996 |
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JP |
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3734096 |
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May 1996 |
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JP |
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3349286 |
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Aug 1996 |
|
JP |
|
2009047989 |
|
Mar 2009 |
|
JP |
|
2009198967 |
|
Sep 2009 |
|
JP |
|
Other References
Abstract of JP 08-123198 published May 17, 1996. cited by applicant
.
Abstract of JP 08-211723 published Aug. 20, 1996. cited by
applicant .
Abstract of JP 08-036294 published Feb. 6, 1996. cited by applicant
.
Abstract of JP 2009-198967 published Sep. 3, 2009. cited by
applicant .
Abstract of JP 2009-047989 published Mar. 5, 2009. cited by
applicant.
|
Primary Examiner: Chen; Sophia S
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Claims
What is claimed is:
1. A developing device, comprising: a developing part configured to
include a developer carrier which is arranged in a vicinity of an
image carrier, and which is rotatable for circulating a developer
inside the developing part and for supplying the developer to the
image carrier; a developer supply member which is rotatable and
carries and supplies the developer to the developer carrier; and a
developer collection member which collects the developer which is
not used to develop an image; a developer stirring part configured
to be arranged at a different position from a position of the
developing part; a developer conveyance part configured to carry
the developer by an air conveyance in a developer conveyance path
from the developer stirring part to the developing part, in which
the developer being circulated in the developing part returns to
the developer stirring part through a developer ejection flow path;
and a developer detection part configured to include an opening
which communicates between the developer supply member and the
developer collection member, to be arranged at a downstream side in
a flow direction of the developer from the opening below and near
the developer supply member, and to detect whether the developer
exists in a vicinity of the developer supply member.
2. The developing device as claimed in claim 1, wherein the
developer detection part is arranged to incline toward the
opening.
3. The developing device as claimed in claim 1, further including a
second opening which communicates between the developer supply
member and the developer collection member at the downstream of the
flow direction of the developer in the developer supply member from
the developer detection part.
4. The developing device as claimed in claim 3, wherein the
developer detection part detects that the developer does not exist
with an additional amount with respect to a lower limit of a
conveyance amount of the developer, the lower limit being where an
excess developer is depleted in the developing part, and the
opening is formed to have an area for assuring the additional
amount.
5. The developing device as claimed in claim 3, further comprising
a second developer detection part configured to be arranged above
and near the developer supply member and at a position
corresponding to the second opening, and to detect whether the
developer exists in a vicinity of the developer supply member.
6. The developing device as claimed in claim 5, wherein the
conveyance amount of the developer carried by the developer
conveyance part to the developing part is controlled based on
detection results of the developer detection part and the second
developer detection part.
7. The developing device as claimed in claim 1, wherein the
conveyance amount of the developer, which is carried by the
developer conveyance part to the developing part, is controlled
based on a detection result of the developer detection part.
8. The developing device as claimed in claim 7, wherein when the
developer detection part detects that the developer does not exist
in the vicinity of the developer supply member, the conveyance
amount of the developer carried by the developer conveyance part to
the developing part is increased.
9. The developing device as claimed in claim 7, wherein the
developer conveyance part includes an air pump and increases the
conveyance amount of the developer by increasing an air supply
amount of the air pump.
10. The developing device as claimed in claim 7, wherein the
developer conveyance part includes a rotary re-feeder and increases
the conveyance amount of the developer by increasing a number of
rotations of the rotary re-feeder.
11. An image forming apparatus, comprising the developing device as
claimed in claim 1.
12. A developing device, comprising: a developing part configured
to include a developer carrier which is arranged in a vicinity of
an image carrier, and which is rotatable for circulating a
developer inside the developing part and for supplying the
developer to the image carrier; and a developer supply member which
is rotatable and carries and supplies the developer to the
developer carrier; a developer stirring part configured to be
arranged at a different position from a position of the developing
part; a developer conveyance part configured to carry the developer
by an air conveyance in a developer conveyance path from the
developer stirring part to the developing part, in which the
developer being circulated in the developing part returns to the
developer stirring part through a developer ejection flow path; and
a powder surface detection part configured to detect a powder
surface of the developer contained in the developing part in a
vicinity of and below the developer supply member, wherein a
conveyance amount of the developer carried by the developer
conveyance to the developing part is controlled so that a
fluctuation width of an output value of the powder surface
detection part exceeds a set value, and wherein a distance between
the powder surface detection part and the developer supply member
is set to be a pumped-up amount in which the developer is not
depleted on the developer carrier.
13. The developing device as claimed in claim 12, wherein the
developer supply member is a screw, and an external diameter of the
developer supply member positioned above the powder surface
detection part is formed to be smaller than other regions.
14. The developing device as claimed in claim 12, wherein the
developer supply member is a screw and a shaft diameter positioned
above the powder surface detection part is formed to be smaller
than other regions.
15. The developing device as claimed in claim 12, wherein the
fluctuation width of the output value of the powder surface
detection part is determined based on a maximum value and a minimum
value when the developer supply member rotates once.
16. The developing device as claimed in claim 12, wherein the
developer conveyance part includes an air pump, and the conveyance
amount of the developer is increased by increasing an air supply
amount of the air pump.
17. An image forming apparatus, comprising the developing device as
claimed in claim 12.
18. A developing device, comprising: a developing part configured
to include a developer carrier which is arranged in a vicinity of
an image carrier, and which is rotatable for circulating a
developer inside the developing part and for supplying the
developer to the image carrier; and a developer supply member which
is rotatable and carries and supplies the developer to the
developer carrier; a developer stirring part configured to be
arranged at a different position from a position of the developing
part; a developer conveyance part configured to carry the developer
by an air conveyance in a developer conveyance path from the
developer stirring part to the developing part, in which the
developer being circulated in the developing part returns to the
developer stirring part through a developer ejection flow path; and
a powder surface detection part configured to detect a powder
surface of the developer contained in the developing part in a
vicinity of and below the developer supply member, wherein a
conveyance amount of the developer carried by the developer
conveyance to the developing part is controlled so that a
fluctuation width of an output value of the powder surface
detection part exceeds a set value, and wherein when it is detected
that the fluctuation width of the output value of the powder
surface detection part tends to decrease, the conveyance amount
carried by the developer conveyance part to the developing part is
increased.
19. The developing device as claimed in claim 18, wherein the
developer conveyance part includes a rotary re-feeder, and the
conveyance amount of the developer is increased by increasing a
rotation of the rotary re-feeder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming
apparatus such as a copier, a facsimile machine, a printer, or the
like applying an electrophotographic method to form an image by
using toner, and more particularly to operations control of a
developing device.
2. Description of the Related Art
A developing device included in an image forming apparatus applying
an electrophotographic method develops and visualizes an
electrostatic latent image formed on an image carrier by using a
developer including two components: toner and a carrier. In the
developing device, in which a developing process ends in a
developing area and the toner is consumed, the developer is
collected and is used again for developing an image after being
mixed and stirred with replenished toner. The developer used for
the developing device is needed to maintain a constant toner
density and charge quantity in order to acquire a stable toner
image. The toner image is adjusted with the consumed toner for
image formation and the replenished toner. The charge quantity is
given by a frictional charge when the toner is mixed with the
carrier. In the developing device using the developer including the
two components, the toner is sufficiently mixed with the carrier to
achieve a uniform toner density distribution, and also the toner
image is stabilized by charging the toner.
In a general-purpose developing device, the toner is distributed
and charged by using a stirring effect of a rotation of two screws
within a short time until the replenished toner is pumped up to a
developing roller. Especially, in a case of consuming a large
amount of toner, the replenished toner is pumped up to the
developing roller before being sufficiently distributed.
Accordingly, image quality is degraded due to toner scattering or
the like.
To solve this problem, a developing device, in which stirring
performance is improved by separating a developing part from a
developer stirring part, is known. Advantageously, in this
developing device, compared with a developing device which conducts
stirring and conveying by using a screw, an amount of toner which
is not charged or not sufficiently charged becomes smaller, and
toner scattering and background fouling occur less. However, since
the developing part and the developer stirring part are separately
arranged, a developer circulation part for circulating the
developer is needed between the developing part and the developer
stirring part. As the developer circulation part, Japanese Patents
No. 3734096 and No. 3349286 disclose conveying mechanism using an
air pump or a mohno pump.
In a case of successively carrying the developer in the tube by
using the air, a conveyance amount may fluctuate depending a state
of the developer. For example, powder characteristics of the
developer are changed depending on a deterioration level,
temperature, moisture, and the like of the developer. When a
developer capacity of the developing part is decreased due to a
decrease of the conveyance amount of the developer, the developer
amount to be pumped up to the developing roller becomes
insufficient and an image defect occurs. Especially, in a case in
which a one-way circulation system is applied to the developing
device, the developer is supplied to the developing roller from a
supply screw arranged parallel to the developing roller, and the
developer being supplied is carried to a collection screw after an
imaging operation. The developer amount in a vicinity of the supply
screw becomes less toward a downstream side of a flow direction of
the developer (a volume decreases more). Accordingly, when the
conveyance amount of the developer decreases, a depletion state
occurs, in which the developer is not supplied to the developing
roller at the downstream side in the flow direction of the
developer. To prevent the occurrence of the depletion state
beforehand, it may be considered to control the conveyance amount
of the developer by detecting the developer amount in the vicinity
of the supply screw.
Accordingly, a powder surface and the volume of the developer in
the imaging device may be detected, and the conveyance amount of
the developer may be controlled based on a detection result.
Japanese Laid-open Patent Applications No. H08-36294 and No.
2009-198967 disclose a developing device using a piezoelectric
oscillation element or a magnetic permeability detection
method.
In the above-described technologies, the piezoelectric oscillation
element is used to detect whether the powder surface of the
developer is higher than a predetermined height. However, the
supply screw and the collection screw are provided. Thus, in the
developing device in which the developer supplied from the supply
screw to the developing roller is not supplied again to the
developing roller, the powder surface of the developer at a
downstream side of the supply screw is significantly lower than
that at an upstream side of the supply screw. The powder surface
fluctuates along a slope of a screw, and thus, is not constant.
Thus, these problems make an output of the powder surface unstable
and a detection of the powder surface becomes difficult. Also, in a
case in which a magnetic permeability sensor is used as a powder
surface detection part, since both the powder surface and the toner
density change, the powder surface is not detected if the toner
density is not accurately recognized.
As described above, the developing device included in the image
forming apparatus of the electrophotographic method is known in
which the developing part and the developer stirring part are
separately arranged and a stirring performance is improved. Since
the developing part and the developer stirring part are separately
arranged, developer circulation part for circulating the developer
is needed between the developing part and the developer stirring
part. As the developer circulation part, the conveying mechanisms
using the air pump or the mohno pump are known.
A developer conveyance by air is influenced by bulk density,
fluidity, toner density, and the like of the developer and the
conveyance amount fluctuates. A developer balance between the
developing part and the developer stirring part is changed.
Especially, when the conveyance amount decreases and a developer
capacity of the developing part decreases, a volume of the
developer for the screw to be supplied to the developing roller is
decreased, and the developer is not sufficiently supplied to the
developing roller. An amount of the developer being pumped up is
decreased at a downstream side of the developing roller after the
developer passes a doctor blade. As a result, an image density
irregularity may occur. Also, due to the decrease of the developer
capacity of the developing part, an amount of the developer of the
developer stirring part increases. Thus, a torque driving a
stirring member is increased and a load becomes greater.
Accordingly, it is needed to control a circulation amount of the
developer to be constant, to stabilize the pumped-up amount and the
developer balance between the developing part and the developer
stirring part.
In order to maintain a height of a powder surface of the developer
at the downstream side of the supply screw, regardless of an image
to be formed, Japanese Laid-open Patent Application No. 2009-47989
discloses a developing device which controls a developer supply
amount for the developing part based on a number of pixels to be
written, a detection result of the toner density by a toner density
detection part, a toner amount to be replenished in the externally
arranged developing stirring part, and a driving time of the
developing device. This technology is effective to increase and
decrease an average conveyance amount due to the toner density and
the fluidity of the developer.
However, as illustrated in FIG. 1, the developer conveyance using
the air is performed in which the conveyance amount is carried with
fluctuation (pulsation) at a shorter interval. When the powder
surface is temporarily lowered due to the pulsation of the
conveyance amount, the developer conveyance may not be sufficiently
performed for this case. It has been known that a scale of the
pulsation depends on conveyance conditions such as the fluidity, a
supply amount of the air, and the like of the developer. When the
supply amount of the air is increased or a rotation of the rotary
re-feeder is increased to increase the conveyance amount, the
pulsation becomes greater in response to these increases. Also,
since the pulsation of the powder surface becomes greater, the
powder surface fluctuates. It becomes difficult to accurately
detect and control the powder surface.
To correspond to a change of the conveyance amount of the developer
due to the pulsation, it is required to detect the powder surface
and the volume of the developer in the developing device, and to
control the conveyance amount of the developer using the air based
on a detection result. Japanese Laid-open Patent Applications No.
H08-36294 and No. 2009-198967 disclose a developing device using a
piezoelectric oscillation element or a magnetic permeability
detection method.
SUMMARY OF THE INVENTION
The present invention solves or reduces one or more of the above
problems.
In one aspect of this disclosure, there is provided a developing
device, including a developing part configured to include a
developer carrier which is arranged in a vicinity of an image
carrier, and which is rotatable for circulating a developer inside
the developing part and for supplying the developer to the image
carrier; a developer supply member which is rotatable and carries
and supplies the developer to the developer carrier; and a
developer collection member which collects the developer which is
not used to develop an image; a developer stirring part configured
to be arranged at a different position from a position of the
developing part; a developer conveyance part configured to carry
the developer by an air conveyance in a developer conveyance path
from the developer stirring part to the developing part, in which
the developer circulated in the developing part returns to the
developer stirring part through a developer ejection flow path; and
a developer detection part configured to include an opening which
communicates between the developer supply member and the developer
collection member, to be arranged at a downstream side in a flow
direction of the developer from the opening below and near the
developer supply member, and to detect whether the developer exists
in a vicinity of the developer supply member.
In another aspect of this disclosure, there is provided a
developing device, including a developing part configured to
include a developer carrier which is arranged in a vicinity of an
image carrier, and which is rotatable for circulating a developer
inside the developing part and for supplying the developer to the
image carrier; and a developer supply member which is rotatable and
carries and supplies the developer to the developer carrier; a
developer stirring part configured to be arranged at a different
position from a position of the developing part; a developer
conveyance part configured to carry the developer by an air
conveyance in a developer conveyance path from the developer
stirring part to the developing part, in which the developer
circulated in the developing part returns to the developer stirring
part through a developer ejection flow path; and a powder surface
detection part configured to detect a powder surface of the
developer contained in the developing part in a vicinity of and
below the developer supply member, wherein a conveyance amount of
the developer carried by the developer conveyance to the developing
part is controlled so that a fluctuation width of an output value
of the powder surface detection part exceeds a predetermined
value.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following, embodiments of the present invention will be
described with reference to the accompanying drawings.
FIG. 1 is a graph for explaining that a conveyance amount of the
developer fluctuates when the developer is carried by air;
FIG. 2 illustrates a schematic front view of an image forming
apparatus in which a developing device according to a first
embodiment is applicable;
FIG. 3 illustrates a schematic perspective view of the developing
device according to the first embodiment;
FIG. 4 illustrates a front view of a developing part used in the
first embodiment;
FIG. 5 illustrates a first configuration of the developing part in
the first embodiment;
FIG. 6 illustrates a schematic view of a developer stirring part
used in the first embodiment;
FIG. 7 illustrates a schematic view of a flow of developer in the
first embodiment;
FIG. 8 illustrates a schematic view for explaining a behavior of
the developer in the developing part in the first embodiment;
FIG. 9 illustrates the behavior of the developer in the developing
part in the first embodiment;
FIG. 10 illustrates a second configuration of the developing part
in the first embodiment;
FIG. 11 illustrates a schematic view for explaining a behavior of
developer in the second configuration in the first embodiment;
FIG. 12 illustrates a schematic view for explaining the behavior of
the developer in the second configuration in the first
embodiment;
FIG. 13 illustrates a variation of the second configuration of the
developing part in the first embodiment;
FIG. 14 illustrates a schematic perspective view of a developing
device according to a second embodiment;
FIG. 15 illustrates a schematic front view of a developing part
used in the second embodiment;
FIG. 16 illustrates a schematic perspective view of the developing
part used in the second embodiment;
FIG. 17 illustrates a schematic view of a developer stirring part
used in the second embodiment;
FIG. 18A through FIG. 18D illustrate a relationship between a
height of a powder surface of the developer and an output value of
a powder surface detection part in the second embodiment;
FIG. 19 is a graph illustrating a relationship between a
fluctuation width of an output value of the powder surface
detection part used in the second embodiment and the height of the
powder surface of the developer;
FIG. 20A and FIG. 20B illustrates schematic views of a conveyance
screw used in the second embodiment;
FIG. 21 is a flowchart for explaining a conveyance amount control
for the developer in a case in which a reference value is set to be
zero in the second embodiment;
FIG. 22 is a graph illustrating a relationship between the height
of the powder surface of the developer and a conveyance amount of
the developer toward the developing part in the second embodiment;
and
FIG. 23 is a flowchart for explaining the conveyance amount control
for the developer in a case in which the reference value is set to
be .DELTA.V2 in the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the following, an embodiment of the present invention will be
described with reference to the accompanying drawings.
FIG. 2 is a diagram illustrating an image forming apparatus in
which a developing device according to a first embodiment is
applicable. In FIG. 2, the image forming apparatus 1 is regarded as
a tandem type of an image forming apparatus, and includes imaging
units 3Y, 3M, 3C, and 3K corresponding to yellow (Y), magenta (N),
cyan (C), and black (K) down below an intermediate transfer belt 2.
The imaging units 3Y, 3M, 3C, and 3K have similar configurations
including photosensitive drums 4 as image carriers, charging parts
5, developing parts 6 forming developing devices, primary transfer
members 7, cleaning devices 8, and the like.
In the image forming apparatus 1, when an imaging operation starts,
the photosensitive drums 4 are uniformly charged by the charging
parts 5. Next, electrostatic latent images, which correspond to an
image to be formed by a writing unit (not shown) are formed on
surfaces of the photosensitive drums 4. Then, toner images
respective to colors are formed on the photosensitive drums 4 by
supplying the toner to the electrostatic latent images from the
developing parts 6. Toner images of respective colors formed on the
photosensitive drums 4 are superimposedly transferred onto the
intermediate transfer belt 2, thereby forming a full color toner
image of four colors on the intermediate transfer belt 2. The full
color toner image is transferred onto a paper sheet, which is
supplied by a feeding roller, a registration roller, and the like
from a feeding cassette 9, by a secondary transfer member 10. The
paper sheet, onto which the toner image is transferred, is passed
through a fixing part 11 to be heated and pressed. After the toner
image is fixed by heat and pressure, the paper sheet is ejected by
an ejection part 12. After the toner image is transferred, the
cleaning devices 8 eliminate residual toner on surfaces of the
respective photosensitive drums 4, and a belt cleaning device 13
eliminates residual toner on the surface of the intermediate
transfer belt 2.
In the image forming apparatus 1, the developing device has the
following features. In a general-purpose developing device, the
toner and a carrier of a developer used to develop an image are
stirred and mixed in a developing unit. In the developing device in
the embodiment, developer stirring parts 14 are arranged separately
from the developing parts 6 provided respectively in the imaging
units 3Y, 3M, 3C, and 3K. The developer stirring parts 14 certainly
stir and mix the developer and replenished toner, and stably
conduct toner distribution and charging. By operations of the
developer stirring parts 14, toner density and toner charges are
stabilized. Accordingly, a preferable image formation is stably
performed. After an imaging operation, the developer is carried
through developer ejection flow paths 15 from the developing parts
6 to the developer stirring parts 14. In the developing stirring
parts 14, new toner is replenished, and the sufficiently stirred
developer is ejected by predetermined amounts by rotary feeders
(not shown). The ejected developer is carried by air pressure from
air pumps 16 regarded as developer conveyance parts, and is
returned to the developing parts 6 via developer conveyance paths
17. The new toner is replenished to the developer stirring parts 14
by small amounts from toner hoppers (or toner cartridge) 18. In
FIG. 2, air suction openings 19 are provided to respective air
pumps 16, an external air suction path 20 is used to suction the
external air, an air dryer 21 is used to dry the external air, and
an air intake part 22 is used to take in the external air.
FIG. 3 is a diagram illustrating a developing device 23 according
to the first embodiment. As described above, the developing device
23 includes the developing part 6 oppositely arranged in a vicinity
of the photosensitive drum 4, and the developer stirring part 14
arranged separately from the developing part 6. The developer is
carried from the developer stirring part 14 to the developer part 6
through the developer conveyance path 17. The developer, in which
the toner and the carrier are mixed, is used. Hereinafter, the
developer is called a two-component developer.
The developer is carried by air conveyance from the developer
stirring part 14 and is supplied to the developing part 6. The
developer falls by gravity in the developer ejection flow path 15
connecting the developing part 6 and the developer stirring part 14
and returns to the developing part 6. Thus, the developer is
circulated between the developing part 6 and the developer stirring
part 14. The developer ejection flow path 15 is formed by a
flexible member such as a silicone tube or the like to be a tube
shape.
As illustrated in FIG. 4, the developer part 6 includes a
developing roller 27 and two conveyance screws 28 and 29 as a
developer carrier in a casing 30. A magnet is provided inside the
developing roller 27. This configuration is well known in which the
developer is suctioned and carried so that the toner is adhered to
the electrostatic latent image formed on the surface of the
photosensitive drum 4. The conveyance screw 28, which is regarded
as a developer supply member, is driven to rotate to carry the
developer from a front to a rear thereof in FIG. 4. The conveyance
screw 29, which is regarded as a developer collection member, is
driven to rotate so as to carry the developer from a rear to a
front thereof. A divider 31 is provided to divide the inside of the
casing 30 into two spaces. The screws 28 and 29 are arranged
respectively in the two spaces. The developing roller 27 and the
conveyance screws 28 and 29 are driven to rotate by a motor (not
shown) through a drive propagation mechanism (not shown).
As illustrated in FIG. 5, the divider 31 includes an opening 25 at
a rear end thereof (FIG. 4), and is formed so that the developer is
moved from the conveyance screw 28 toward the conveyance screw 29.
A supply opening 26 of the developer is provided at an edge of a
front side in FIG. 4. In the casing 30 positioned at a vicinity of
a peripheral surface of the developer roller 27, a doctor blade 32
is arranged to regulate the developer attached to the developing
roller 27 in a certain amount.
As illustrated in FIG. 3 and FIG. 6, in the developer stirring part
14, a casing 35 is provided to contain the developer and have a
shape in which a diameter becomes narrower toward a bottom. A
developer replenishing opening 33 is provided at an upper portion
of the casing 35 and an ejection opening 34 is provided at a lower
portion of the casing 35. Inside the casing 35, a screw 36 is
provided to carry the developer from down to up, and a pair of
stirring members 37 is rotatably provided. The screw 36 is arranged
at a center position of the casing 35. The stirring members 37 are
symmetrically arranged outside the screw 36. The screw 36 and the
stirring members 37 are alternately rotated. Thus, the developer in
the casing 35 is mixed.
The screw 36 and the stirring members 37 are driven and rotated by
a motor 38 regarded as the developer conveyance part. The screw 36
is connected to the motor 38, and each of the stirring members 37
is decelerated and rotated via a deceleration gear sequence formed
by multiple gears 39. The developer is carried due to gravity from
a developer replenishing opening 33 to the ejection opening 34.
Thus, the developer is always in the developer stirring part 14.
That is, a non-mixed developer may not be ejected. The developer
pumped upward from a bottom by a rotation of the screw 36 is
transferred downward along rotations of the stirring members 37
which rotate outside the screw 36, and is collected around the
screw 36, again. As described above, the developer is always
circulated in the casing 35. By circulating the developer, the
entire developer inside the casing 35 is uniformly mixed.
Also, in the first embodiment, the two-component developer is
applied. Since a charge of the toner is applied by friction with
the carrier, it is important to improve contact efficiency between
the toner and the carrier in order to rapidly acquire a charge
amount. By investigations of the inventors of the present
invention, it is proved that the contact efficiency inside the
casing 35 is improved by circulating the developer and a problem
related to the developer occurs less. The new toner is replenished
by the toner hopper 18 to the casing 35 based on consumption of the
toner. That is, the motor 40 is driven to rotate a conveyance screw
of a small size (not shown) arranged in a toner supply path 41 and
the new toner in the toner hopper 18 is carried into the casing 35.
The conveyance screw of the small size (not shown) is formed
capable of carrying a certain amount of the new toner contained in
the toner hopper 18 by being rotated. A replenished amount of the
new toner is determined by a control part (not shown) depending on
a detection result of a toner density sensor (not shown) which is
attached near the most downstream position in a flow direction of a
collected developer in the conveyance screw 29.
Below the developer stirring part 14, as illustrated in FIG. 6, a
rotary re-feeder 42 is arranged as the developer conveyance part to
be communicated to the casing 35. The rotary re-feeder 42 includes
a function for ejecting a certain amount of the developer from the
casing 35. The rotary re-feeder 42 includes a casing 43 and a blade
wheel 44 rotatably provided in the casing 43. The certain amount of
the developer is ejected downward by the blade wheel 44 being
rotated by the motor 45 illustrated in FIG. 3.
A confluence part 46 is provided downward of the blade wheel 44.
The confluence part 46 is connected to an air path 47 connected to
a supply opening of the air pump 16 and an entrance part 48
regarded as one end of the developer conveyance path connected to
the developing part 6. The developer of the certain amount ejected
by the blade wheel 44 is carried by the air conveyance from the air
pump 16 to the developing part 6. That is, the developer of the
certain amount ejected from the rotary re-feeder 42 is returned to
the developing part 6 by air pressure supplied by the air pump 16
inside the developer conveyance path 17. The developer conveyance
path 17 is formed to be a tube shape by a material such as silicon
or the like.
As illustrated in FIG. 5, a developer G (FIG. 7) having inflowed
from the supply opening 26 via the developer conveyance path 17 is
carried in a flow direction B of the replenished developer by the
conveyance screw 28, and also is supplied to the developing roller
27 while a thickness is regulated by the doctor blade 32 as
illustrated in FIG. 7. The developer (excess developer) which is
not supplied to the developing roller 27 falls into the conveyance
screw 29 from the opening 25 illustrated in FIG. 5. The conveyance
screw 29 receives the collected developer carried from the
conveyance screw 28 and carries the collected developer in a flow
direction A of the collected developer. The collected developer is
ejected from an ejection part 24 and is transferred to the
developer stirring part 14 through the developer ejection flow path
15.
Features of the present invention will be described. First, a
volume of the developer in the developing part 6 will be described.
In the developing part 6 of a one direction circulation method as
illustrated in FIG. 5, since the developer is consumed in
accordance with the flow direction B from an upstream side to a
downstream side in the conveyance screw 28, a volume of the
developer becomes less from the upstream to the downstream. On the
other hand, in the conveyance screw 29, the volume of the developer
becomes more toward the upstream side in the flow direction A
(limited in an area of the developing width) Accordingly, if the
developer comes to have a shortage at the downstream in the flow
direction A in the conveyance screw 29, a depletion state occurs in
the conveyance screw 29. As a result, the developer may not be
supplied to the developing roller 27.
In order to prevent the above-described problem, in general, the
developer is excessively supplied not to be depleted. However, in
the first embodiment, the developer is carried by the air
conveyance from outside of the developing part 6. Thus, a
conveyance amount may fluctuate depending on a state of the
developer (a toner density, an environmental condition,
deterioration state, and the like). If the conveyance amount
decreases, the depletion state may occur. The occurrence of the
depletion state is prevented by detecting the decrease of the
conveyance amount beforehand. It is effective to detect the volume
of the developer in a vicinity of the conveyance screw 28. As
described in BACKGROUND OF THE INVENTION, a powder surface of the
developer may not be accurately comprehended. However, a presence
or an absence of the developer is easily detectable in a digital
method (in a binary method), and may be accurately comprehended. In
a first configuration in the first embodiment for a method for
detecting the depletion state beforehand by a binary method, as
illustrated in FIG. 5, a sensor 49 is arranged as a developer
detection part at a downstream position near the opening 25 in the
flow direction B. As the sensor 49, a piezoelectric sensor using a
piezoelectric element, a magnetic permeability sensor for detecting
a magnetic permeability of the developer, an electrostatic capacity
sensor, and the like are usable.
An image area (developing width) 9a is regarded as an area in which
the developer is required and the depletion state is not to be
detected beforehand. The sensor 49 is set at a position in an area
excluding the image area and areas other than the image area in
which the depletion state is not detectable when the developer on
the sensor 49 is exhausted. The sensor 49 is positioned in the area
in which the occurrence of the depletion state is surely detectable
when the developer on the sensor 49 is exhausted. FIG. 8
illustrates a state in which the depletion of the developer does
not occur, and FIG. 9 illustrates a state in which the conveyance
amount of the developer decreases (the depletion of the developer
may occur).
In a state illustrated in FIG. 8, a portion of excess developer
falls from the opening 25. Another portion of the excess developer
is carried over the opening 25 and moves an end of the conveyance
screw 28, and is detected by the sensor 49. In a case in which the
conveyance amount of the developer is gradually decreased, a method
for detecting the depletion state beforehand will be described.
When the conveyance amount of the developer is decreased, an amount
of the excess developer is decreased, and all excess developer
falls through the opening 25. In this case, the developer does not
exist on the sensor 49. The sensor 49 outputs information
indicating that no developer exists. When the developer further
decreases and the depletion occurs, it is possible to comprehend a
decrease state of the developer before the depletion occurs.
By the above-described simple configuration, it is possible to
certainly detect the occurrence of the depletion state of the
developer. When it is detected based on a detection result of the
sensor 49 that the developer does not exist in a vicinity of the
conveyance screw 28, it is possible to control the conveyance
amount of the developer toward the developing part 6 by the
developer conveyance part. That is, by increasing an air supply
amount of the air pump 16, a number of rotations of the motor 38, a
rotation of the rotary re-feeder 42, and the like, a developer
amount is increased to carry to the developing part 6. Accordingly,
it is possible to stably and successively supply the developer
surely to the developing roller 27, and it is possible to
successively perform a preferable image formation. In the
above-described configuration, as illustrated in FIG. 5, FIG. 8,
and FIG. 9, the sensor 49 is arranged to incline toward the opening
25. Since the developer on the sensor 49 falls through the opening
25 by gravity when the developer decreases, it is possible to
prevent a detection error due to residual developer on the sensor
49. Accordingly, a state in which the developer does not exist
becomes surely detectable.
FIG. 10 illustrates a second configuration in the first embodiment.
In the second configuration, a second opening 50 is provided at a
position downstream more than the sensor 49 in the flow direction B
of the replenished developer for the conveyance screw 28. In the
second configuration, FIG. 11 illustrates a state in which the
depletion does not occur, and FIG. 12 illustrates a state in which
the conveyance amount of the developer decreases (the depletion may
occur soon). In the state illustrated in FIG. 11, a portion of the
excess developer falls from the opening 25. The residual developer
is carried to a side of the sensor 49, and further falls from the
opening 50 to the conveyance screw 29. As illustrated in FIG. 12,
when the conveyance amount of the developer becomes even less, the
developer falls only from the opening part 25. Then, no developer
exists on the sensor 49. In this configuration, when it is detected
that the developer does not exist in the vicinity of the conveyance
screw 28 based on the detection result of the sensor 49, by
increasing the developer amount carried to the developing part 6,
it is possible to acquire an effect similar to the first
configuration.
In the second configuration, an area of the opening 25 may be
formed to have a size for the excess developer to pass (fall) so
that the developer, which is assured as an additional amount with
respect to the conveyance amount (flow amount) of the developer
being a depletion lower limit, is retained in the developing part
6. It is assumed that when a regular conveyance amount of the
developer is 100 g/sec, the depletion lower limit (essential amount
to develop an image) of the developer is 80 g/sec, and the
conveyance amount of the developer assured as the additional amount
is 10 g/sec, an area of the opening 25 is formed to be an area for
the developer of 10 g/sec to pass. Also, the sensor 49 is formed to
output information indicating that no developer exits when the
conveyance amount of the developer becomes less than 90 g/sec. In
detail, in a case in which the conveyance amount of the developer
is 100 g/sec (the excess developer of 20 g/sec), the developer of
10 g/sec falls from the opening 25 and the residual developer of 10
g/sec passes on the sensor 49 and falls from the second opening 50,
and the conveyance amount of the developer is 90 g/sec (the excess
developer of 10 g/sec), the developer of 10 g/sec falls from the
opening 25. Thus, the developer is not carried onto the sensor 49,
and the sensor 49 outputs the information indicating that the
developer does not exist. As described above, the area of the
opening 25 is formed to retain the additional amount with respect
to the conveyance amount of the developer, which is nearly the
depletion state, in the developing part 6. It is possible to
accurately set the additional amount in the conveyance amount of
the developer and to certainly detect the occurrence of the
depletion state of the developer.
FIG. 13 illustrates a variation of the second configuration. In the
variation, different from the second configuration, at a position
which is in a vicinity and above the conveyance screw 28 and is
opposite to the second opening 50, a sensor 51 is provided as a
second developer detection part for detecting whether the developer
exists in the vicinity of the conveyance screw 28. Each of the
first and second configurations is regarded to correspond to the
problem caused in a case in which the conveyance amount of the
developer decreases. However, if the conveyance amount increases,
the developer does not drop well from the opening 25 and the second
opening 50, and the developer may clog an end of the conveyance
screw 28. In a case in which the developer clogs the end, a
conveyance of the developer by the conveyance screw 28 may create a
problem. Not only a malfunction of the imaging operation may occur
but also the developing part 6 may have an error. In this case,
since the developer contacts the sensor 51, it is possible to
detect the occurrence of the above problem beforehand. In a case of
detecting the developer by the sensor 51, by decreasing the air
supply amount of the air pump 16, the rotation of the motor 38, the
rotation of the rotary re-feeder 42, and the like, the developer
amount, which is to be carried to the developing part 6, is
decreased. Accordingly, it is possible to successively conduct the
preferable image formation.
In the first embodiment, a color printer is exemplified as the
image forming apparatus. The image forming apparatus to which the
first embodiment is applied is not limited to the color printer.
Also, the first embodiment is applicable for a copier, a plotter, a
facsimile machine, a multi-functional apparatus including these
functions, and the like.
According to the first embodiment, it is possible to certainly
detect the depletion of the developer by the above-described simple
configuration. Also, it is possible to provide the developing
device realizing a stable conveyance amount of the developer.
According to the present invention, it is possible to certainly
detect the occurrence of the depletion state of the developer by
the above-described simple configuration. By controlling the
conveyance amount of the developer carried by the developer
conveyance part to the developing part based on a detection result
of the developer detection part, it is possible to certainly and
successively conduct a stable supply of the developer for the
developer carrier and realize successively performing the
preferable image formation.
In the following, the developing device according to a second
embodiment will be described. An image forming apparatus, in which
the developing device according to the second embodiment is
applicable, may be the same as the image forming apparatus 1 in
FIG. 2. In the second embodiment, the components that are the same
as those in the first embodiment are indicated by the same
reference numerals and the explanation thereof will be omitted.
FIG. 14 illustrates a schematic perspective view of a developing
device 23-2 according to the second embodiment. The developing
device 23-2 includes a developing part 6-2 being oppositely
arranged in a vicinity of the photosensitive drum 4, and the
developer stirring part 14 arranged separately from the developing
part 6-2. The developer is carried from the developer stirring,
part 14 to the developing part 6-2 through the developer conveyance
path 17 and a developer feed hole 124. The two-component developer
in which the toner and the carrier are mixed may be used as the
developer.
The developer is carried by air conveyance from the developer
stirring part 14 and is supplied to the developing part 6-2 from
the developer feed hole 124. The developer falls by gravity in the
developer ejection flow path 15 connecting the developing part 6-2
and the developer stirring part 14 and returns to the developer
stirring part 14. Thus, the developer is circulated between the
developing part 6-2 and the developer stirring part 14. The
developer ejection flow path 15 is formed by a flexible member such
as a silicone tube or the like to be tubular in shape.
As illustrated in FIG. 15, the developing part 6-2 includes the
developer roller 27 and the two conveyance screws 28 and 29 as the
developer carrier. The developer roller 27 includes a magnet
inside, and the developer is adhered to and conveyed by the
developing roller 27. The toner is adhered to an electrostatic
latent image formed on a surface of the photosensitive drum 4. The
conveyance screw 28, which is regarded as the developer supply
member, is driven to rotate to carry the developer from a front to
a rear thereof as illustrated in FIG. 15. The conveyance screw 29,
which is regarded as the developer collection member, is driven to
rotate so as to carry the developer from a rear to a front thereof.
A divider 31-2 is provided to divide the inside of the casing 30
into two spaces. The conveyance screws 28 and 29 are arranged
respectively in the two spaces. The developing roller 27 and the
conveyance screws 28 and 29 are driven to rotate by a motor (not
shown) through a drive propagation mechanism (not shown).
As illustrated in FIG. 16, the divider 31-2 includes an opening
25-2 at a rear end thereof (FIG. 16), and is formed so that the
developer is moved from the conveyance screw 28 toward the
conveyance screw 29. The developer is carried toward the conveyance
screw 29 from the conveyance screw 28. The supply opening 26 of the
developer is provided at an edge of a front side in FIG. 16. In the
casing 30 positioned at the vicinity of the peripheral surface of
the developer roller 27, the doctor blade 32-2 is arranged to
regulate the developer attached to the developing roller 27 to the
certain amount.
As illustrated in FIG. 14 and FIG. 17, in the developer stirring
part 14, a casing 35 is provided to contain the developer and have
a shape in which a diameter becomes narrower toward a bottom. The
developer replenishing opening 33 is provided at the upper portion
of the casing 35 and the ejection opening 34 is provided at a lower
portion of the casing 35. Inside the casing 35, a screw 36 is
provided to carry the developer from down to up, and two stirring
members 37 are rotatably provided. The screw 36 is arranged at the
center position of the casing 35. The stirring members 37 are
symmetrically arranged outside the screw 36. The screw 36 and the
stirring members 37 are alternately rotated. Thus, the developer in
the casing 35 is mixed.
The screw 36 and the stirring members 37 are driven and rotated by
the motor 38 regarded as the developer conveyance part. The screw
36 is connected to the motor 38. Each of the stirring members 37 is
decelerated and rotated via a deceleration gear sequence formed by
multiple gears 39a, 39b, 39c, and 39d. The developer is carried due
to gravity from the developer replenishing opening 33 to the
ejection opening 34. Thus, the developer is always in the developer
stirring part 14. That is, the non-mixed developer may not be
ejected. The developer pumped upward from a bottom by a rotation of
the screw 36 is transferred downward along rotations of the
stirring members 37 which rotate outside the screw 36, and is
collected around the screw 36, again. As described above, the
developer is always circulated in the casing 35. By circulating the
developer, the entire developer inside the casing 35 is uniformly
mixed.
Also, in the second embodiment, the two-component developer is
applied. Since a charge of the toner is applied by friction with
the carrier, it is important to improve contact efficiency between
the toner and the carrier in order to rapidly acquire a charge
amount. By investigations of the inventors of the present
invention, it is proved that the contact efficiency inside the
casing 35 is improved by circulating the developer and a problem
related to the developer occurs less. New toner is replenished by
the toner hopper 18 (FIG. 14) to the casing 35 based on consumption
of the toner. That is, the motor 40 is driven to rotate a
conveyance screw of a small size (not shown) arranged in a toner
supply path 41 and the new toner in the toner hopper 18 is carried
into the casing 35. The conveyance screw of the small size (not
shown) is formed capable of carrying a certain amount of the new
toner contained in the toner hopper 18 by being rotated. A
replenished amount of the new toner is determined by a control part
(not shown) depending on a detection result of a toner density
sensor (not shown) which is attached near the most downstream
position in a flow direction of a collected developer in a
conveyance screw 29.
Below the developer stirring part 14, as illustrated in FIG. 17, a
rotary re-feeder 42 is arranged as a developer conveyance part to
be communicated to the casing 35. The rotary re-feeder 42 includes
a function for ejecting a certain amount of the developer from the
casing 35. The rotary re-feeder 42 includes a casing 43 and a blade
wheel 44 rotatably provided in the casing 43. The certain amount of
the developer is ejected downward by the blade wheel 44 being
rotated by the motor 45 illustrated in FIG. 14.
A confluence part 46 is provided downward of the blade wheel 44.
The confluence part 46 is connected to an air path 47 connected to
a supply opening of the air pump 16 and an entrance part 48
regarded as one end of the developer conveyance path connected to a
developer feed hole 124 (FIG. 14). The developer of the certain
amount ejected by the blade wheel 44 is carried by the air
conveyance from the air pump 16 to the developer feed hole 124.
That is, the developer of the certain amount ejected from the
rotary re-feeder 42 is returned to the developing part 6-2 by air
pressure supplied by the air pump 16 inside the developer
conveyance path 17. The developer conveyance path 17 is formed to
be a tube shape by a material such as silicon or the like.
Features of the present invention will be described. As illustrated
in FIG. 15, a sensor 49-2 is arranged below and in a vicinity of
the conveyance screw 28 as a powder surface detection part for
detecting whether a height of the powder surface of the developer
carried by the conveyance screw 28 is higher than a predetermined
height. The sensor 49-2 detects the powder surface of the developer
at a downstream in a flow direction of the developer by the
conveyance screw 28. The sensor 49-2 is arranged at an area P
illustrated in FIG. 16 between an end of the downstream in the flow
direction of the developer and the opening 25-2 to which the excess
developer drops toward the conveyance screw 29, in a region in
which the conveyance screw 28 faces the developer roller 27. The
sensor 49-2 is arranged lower than a rotation shaft of the
conveyance screw 28, and detects the powder surface of the
developer in an area 50-2. The magnetic permeability sensor for
detecting the toner density is used as the sensor 49-2, and outputs
a signal corresponding to a ratio of the carrier in the developer
which exists above the sensor 49-2.
A relationship between the powder surface of the developer and the
sensor 49-2 will be described with reference to FIG. 18A through
FIG. 18D. FIG. 18A and FIG. 18C illustrate a relationship between
the powder surface of the developer on the sensor 49-2 and a height
of the blade of the conveyance screw 28. FIG. 18B and FIG. 18D
illustrates a change of the output of the sensor 49-2. FIG. 18A
illustrates a case in which the powder surface is positioned lower
than the blade of the conveyance screw 28. In this case, since the
powder surface does not contact the blade even if the conveyance
screw 28 is rotated, the output of the sensor 49-2 becomes constant
as illustrated in FIG. 18B. FIG. 18C illustrates a case in which
the powder surface is positioned higher than the blade of the
conveyance screw 28. In this case, since the developer is carried
by the slope of the blade of the conveyance screw 28, the height of
the powder surface changes with rotation of the conveyance screw
28. By the rotation of the conveyance screw 28, the power surface
of the developer on the sensor 49-2 becomes the highest in height
immediately before the blade passes on the sensor 49-2, and then
becomes the lowest in height. Accordingly, the output of the sensor
49-2 fluctuates based on a screw rotation period as illustrated in
FIG. 18A through FIG. 18D. In a case in which the magnetic
permeability sensor is used as the sensor 49-2 as illustrated in
the second embodiment, an output value changes depending on the
toner density, but a fluctuation width based on the screw rotation
period hardly depends on the toner density.
FIG. 19 is a diagram illustrating a relationship between the height
of the powder surface of the developer and the fluctuation width of
the output value of the sensor 49-2. As illustrated in FIG. 19,
when the height of the powder surface is lower so as not to contact
the blade of the conveyance screw 28, the output value hardly
changes and the fluctuation width may be zero. However, when the
height of the powder surface becomes higher than a height h which
may be equal to the blade of the conveyance screw 28, the output
value of the sensor 49-2 starts fluctuating depending on the screw
rotation period. The fluctuation width becomes greater in response
to an increase of the height of the powder surface until the height
of the powder surface exceeds a half screw diameter. Thus, based on
the fluctuation width of the output value of the sensor 49-2, it is
determined that the powder surface of the developer is higher than
the blade of the conveyance screw 28. Even if the magnetic
permeability sensor as the sensor 49-2 is used, the fluctuation
width of the output value does not depend on the toner density.
Thus, independent of the toner density, it is possible to determine
that the height of the powder surface of the developer is greater
than a reference value. In this detection method, even if the
developer supply amount for the developing part 6-2 changes in
response to the pulsation, it is possible to detect whether the
developer carried with the conveyance amount of a lower limit value
is retained at more than a predetermined height in the developing
part 6-2.
By the above-described configuration, it is determined by the
sensor 49-2 whether the height of the powder surface of the
developer is greater than a predetermined height. The conveyance
amount of the developer is controlled by controlling operations of
the air pump 16 the motor 38, the rotary re-feeder 42, and the like
as the developer conveyance part, so that the height of the powder
surface is not lower than the predetermined height. Accordingly, it
is possible to prevent the height of the powder surface of the
developer becoming lower at the downstream side in the flow
direction of the developer by the conveyance screw 28. Also, it is
possible to assure a stable amount of the developer for the entire
developer roller 27. Moreover, it is possible to successively
perform preferable image forming operations.
Next, a setting method for setting the height of the powder surface
of the developer which the sensor 49-2 detects will be described. A
relationship between the height of the powder surface of the
developer on the conveyance screw 28 and the supply amount (a
pumped-up amount) of the developer toward the developing roller 27
may be investigated, and the lower limit value may be investigated.
The lower limit value indicates the height of the powder surface in
which the pumped-up amount becomes constant and the depletion of
the developer does not occur on the developing roller 27. Next, a
shape of the blade positioned above the sensor 49-2 is designed, so
that a distance between the blade of the conveyance screw 28 and
the divider 31-2 corresponds to the height indicated by the lower
limit value. In a regular developing device, the distance between
the blade of the conveyance screw 28 and the divider 31-2 is
designed to be approximately 0.5 mm to 2.0 mm to assure the
conveyance amount of the developer. In addition, in order to
acquire a sufficient pumped-up amount of the developer, the height
of the powder surface may be approximately 1/3 screw diameter.
However, in a case in which the distance between the blade and the
divider 31-2 in the entire conveyance screw 28 is expanded to 1/3
screw diameter, a conveyance effect of the conveyance screw 28 is
unfavorably degraded.
Accordingly, a distance between the blade of the conveyance screw
28 positioned above the sensor 49-2 and the divider 31-2 is
expanded to 1/3 screw diameter, and a distance between the blade
and the divider 31-2 at a upstream side of the flow direction of
the developer is set to be 0.5 mm to 2.0 mm. FIG. 20A and FIG. 20B
are diagrams illustrating a magnification of a vicinity of the
sensor 49-2 of the conveyance screw 28. In FIG. 20A, an external
diameter of the blade of the conveyance screw 28 positioned above
the sensor 49-2 is formed to be smaller than that of a region at
the upstream of the flow direction of the developer. In FIG. 20B, a
shaft diameter of the conveyance screw 28 positioned above the
sensor 49-2 is formed to be smaller than that of the region at the
upstream of the flow direction of the developer. As described
above, the distance between the blade of the conveyance screw 28
and the divider 31-2 is expanded, and the distance is set to be
equal to or greater than the height which is the lower limit value
so that the pumped-up amount of the developer becomes constant. The
powder surface of the developer always contacts the blade of the
conveyance screw 28 at a position corresponding to the sensor 49-2.
Therefore, it is possible to prevent the occurrence of the
depletion of the developer due to a shortage of the pumped-up
amount of the developer at the downstream side of the flow distance
of the developer by the developing roller 27. Also, it is possible
to acquire a stable pumped-up amount at the downstream of the flow
direction of the developer by the developing roller 27.
Next, a control method for controlling the conveyance amount of the
developer toward the developing part 6-2 based on the fluctuation
width of the output value of the sensor 49-2 will be described. The
fluctuation width of the output value of the sensor 49-2 is
detected based on the rotation period of the conveyance screw 28.
If the powder surface of the developer is greater than the height
of the blade of the conveyance screw 28, the output value of the
sensor 49-2 fluctuates depending on the rotation period of the
conveyance screw 28. Accordingly, the output value of the sensor
49-2 is monitored at the rotation period of the conveyance screw
28, and the fluctuation width is calculated based on its maximum
value and minimum value. Thus, since the powder surface is detected
within the shortest time, it is possible to timely increase the
supply amount of the developer when the powder surface becomes
lower.
A process flow from detecting the fluctuation width to controlling
the fluctuation width will be described with reference to FIG. 21.
In FIG. 21, the developing device 23-2 is activated and the
developer is stably circulated (step ST01). Then, the output of the
sensor 49-2 is monitored and the fluctuation width of the output
value is calculated (step ST02). In the step ST02, the fluctuation
width is measured ten times at the rotation period of the
conveyance screw 28 and measured fluctuation widths are averaged.
It is determined whether the fluctuation width is greater than zero
(step ST03). When the fluctuation width is greater than zero, it is
determined that the developer is normally circulated, and an
imaging operation starts without changing the conveyance amount of
the developer (step ST04). On the other hand, when the fluctuation
width is equal to zero, it is determined that the conveyance amount
of the developer is insufficient, and the conveyance amount of the
developer is increased (step ST05). By increasing the air supply
amount from the air pump 16 or the rotation of the rotary re-feeder
42, the conveyance amount of the developer is increased.
The conveyance amount of the developer toward the developing part
6-2 and the height of the powder surface are in a proportional
relationship as illustrated in FIG. 22. Thus, by increasing the
conveyance amount of the developer, it is possible to increase the
height of the powder surface of the developer in the vicinity of
the conveyance screw 28. After the conveyance amount of the
developer is increased, the developer is circulated for
approximately 10 seconds until a circulation of the developer
becomes stable. After that, the fluctuation width of the output
value of the sensor 49-2 is calculated again (step ST06), and a
value of the fluctuation width is confirmed (step ST07). When the
fluctuation width is zero, the imaging operation is discontinued
(step ST08). After that, the conveyance amount of the developer is
increased, again (step ST09). The above-described steps are
repeated until the fluctuation width becomes zero. When it is
confirmed that the fluctuation width becomes positive, the imaging
operation is started. The fluctuation width of the sensor 49-2 is
always calculated even in the imaging operation when the developing
device 23-2 is being operated. When the fluctuation width becomes
zero, the imaging operation is discontinued and the conveyance
amount is controlled to be increased. After the fluctuation amount
becomes positive and it is confirmed that the conveyance amount is
sufficiently acquired, the imaging operation is restarted.
In the above-described configuration, by setting the fluctuation
width to be greater than the reference value, it is possible to
prevent an occurrence of a defect in which the imaging operation is
discontinued because of a decrease of the conveyance amount of the
developer in the imaging operation. As the reference value, the
height of the powder surface may be set to retain to be greater
than the lower limit value in which the pumped-up amount is
influenced. In the following, a conveyance amount control for the
developer will be described with reference to FIG. 23 in a case in
which a fluctuation width .DELTA.V2 of the output value of the
sensor 49-2 at a height h2 (h2>lower limit value) of the powder
surface is used. FIG. 23 is a diagram illustrating a flowchart for
explaining a conveyance amount control for the developer in the
case in which the reference value is set to be .DELTA.V2 in the
second embodiment.
In FIG. 23, the developing device 23-2 is activated and the
developer is stably circulated (step ST11). Then, the output of the
sensor 49-2 is monitored and the fluctuation width of the output
value is calculated (step ST12). In the step ST12, the fluctuation
width is measured ten times at the rotation period of the
conveyance screw 28 and measured fluctuation widths are averaged.
It is determined whether the fluctuation width is greater than
.DELTA.V2 (step ST13). When the fluctuation width is equal to or
greater than .DELTA.V2, it is determined that the developer is
normally circulated. Then, the imaging operation starts without
changing the conveyance amount of the developer (step ST14). On the
other hand, when the fluctuation width is less than .DELTA.V2, it
is determined that the conveyance amount of the developer tends to
decrease. Then, the conveyance amount of the developer is increased
(step ST15).
In a case in which the conveyance amount of the developer is
increased, after the developer is circulated for approximately 10
seconds until being stable, the fluctuation width of the output
value of the sensor 49-2 is calculated, again (step ST16), and a
value of the fluctuation width is confirmed (step ST17). When the
fluctuation width is less than .DELTA.V2, it is determined whether
the fluctuation width is greater than zero (step ST18). When the
fluctuation width is positive, the conveyance amount of the
developer is increased (step ST19). When the fluctuation width is
zero, after the imaging operation is discontinued (step ST20), the
conveyance amount of the developer is increased (step ST21). The
above-described steps are repeated until the fluctuation width
becomes positive. When it is determined that the fluctuation width
becomes positive, the imaging operation starts. The fluctuation
width of the sensor 49-2 is always calculated even in the imaging
operation when the developing device 23-2 is being operated. When
the fluctuation width becomes zero, the imaging operation is
discontinued and the conveyance amount is controlled to be
increased. After the fluctuation amount becomes positive and it is
confirmed that the conveyance amount is sufficiently acquired, the
imaging operation is restarted.
In the second embodiment, the height h2 of the powder surface is
higher than the lower limit value. Thus, the pumped-up amount of
the developer on the developing roller 27 may not be insufficient
immediately when the height of the powder surface increases more
than the height h2. The conveyance amount of the developer is
controlled to be increased by detecting that the height of the
powder surface tends to decrease, before the height of the powder
surface decreases at the lower limit value. Therefore, the image
operation may not be discontinued for the conveyance amount
control. However, when the fluctuation width becomes zero, the
imaging operation is discontinued and the conveyance amount of the
developer is increased.
As described above, it is detected whether the height of the powder
surface of the developer is equal to or higher than a predetermined
height, and the conveyance amount of the developer toward the
developing part 6-2 is controlled based on this detection result.
Therefore, it is possible to retain the height of the powder
surface of the developer at the downstream in the flow direction of
the developer by the conveyance screw 28, to be equal to or higher
than the lower limit value. Also, it is possible to effectively
prevent the occurrence of the image density irregularity due to the
fluctuation of the conveyance amount of the developer.
In the second embodiment, a color printer is exemplified as the
image forming apparatus. The image forming apparatus to which the
second embodiment is applied is not limited to the color printer.
Also, the second embodiment is applicable for a copier, a plotter,
a facsimile machine, a multi-functional apparatus including these
functions, and the like.
In the second embodiment, it is detected whether the height of the
powder surface of the developer is equal to or greater than the
predetermined height. An operation of the developer conveyance part
is controlled so that the height of the powder surface becomes less
than the predetermined height. Hence, the conveyance amount of the
developer is controlled. It is possible to prevent an occurrence of
lowering the powder surface of the developer at the downstream in
the flow direction of the developer of the developer supply member.
Also, it is possible to acquire a stable pump-up amount of the
developer in the entire developer carrier and to successively
perform the preferable image forming operations.
Accordingly, it is possible to provide the developing device 23-2
in which the height of the powder surface of the developer at the
downstream of the conveyance screw 28 is retained, regardless of a
scale of the pulsation of the conveyance amount. Also, it is
possible to provide the image forming apparatus 1 including the
developing device 23-2.
The present invention is not limited to the specifically disclosed
embodiments, and variations and modifications may be made without
departing from the scope of the present invention.
The present application is based on the Japanese Priority
Applications No. 2010-247846 filed Nov. 4, 2010 and No. 2010-247850
filed Nov. 4, 2010, the entire contents of which are hereby
incorporated by reference.
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